1. Field of the Invention
The present invention relates to a flexible tube of an insertion apparatus (e.g., an endoscope) which is inserted into a cavity of a passage, and also to an insertion apparatus having the flexible tube.
2. Description of the Related Art
A flexible tube made by providing an outer sheath on the outer side of a helical tube is disclosed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 2013-097327. The helical tube of the flexible tube includes a closely wound region in which a closely wound portion and a sparsely wound portion are alternately arranged in the longitudinal direction. The closely wound portion is a portion where the wire portions adjacent in the longitudinal direction are applied with a tight contact force, and the sparsely wound portion is a portion where the wire portions adjacent in the longitudinal direction are separate from each other.